generator no output

[stockers08]

hi all

i hope this section of the forum is suitable for this.

i have a genset 8/300  welder generator.   8kva 3phase output.

but i cant get it to make any power.     it uses a self excited squirrel cage induction type generator. 

all stator coils measure at 0.9 ohms.    when running at 3100 rpm, im getting less than 1v from any 1 phase to phase.   i have tested the 3 capacitors and they all measure out at 60/61 micro farad.  so spot on their rating.    i have tried flashing on the welder side but no output.   

can anyone help?

 

[stockers08]

i dont know how long but i can only guess so.  just to make it clear, this has NO regulator.   it is self excited induction.  everything i have ready tells me it should gradually build up voltage.  but leaving it running for an hour, its still sat at 1.5v phase to phase.

 

[apprentice87]

What about the single phase and welding outputs??

On the end where the control panel is, on the black bit at the bottom of the machine is a little hatch thing, take that off and there is a pcb board, at least there was on mine!! Check the connections on there.

Used to have an MPM 8/300 years ago, they might have changed since. You will not get much help from Genset, they are both rude and lettuced.. try; 01904 410041 ask for Les Ford. Tis a firm called technical arc.They both make and repair welding sets, if they cannot fix it, no-one can...

john..

 

[stockers08]

i know the pcb you are talking about.  this does not get power untill the generator generates, it is powered via a transformer tapped from phase 3.

being a self excited induction generator, im told there is very little than can go wrong.  you cant burn out coils because the rotor magetic field collapses when over loaded.  ect.  the only thing that can go wrong is the caps, but these metered out to be in good working order.  so thats why i am baffled

 

[apprentice87]

All I can remember about the thing was there was a big bank of diodes and thyristors to control welding output.. The 230V output varied according to the engine speed, i do not think it was regulated... My one did not have a 415V output, just 230V and 110V.

There was a smaller diode connected across the welding output, but orientated so that it would not just short out the set output [Eh!]

This packed up on mine. Genset, [courgette you *****] were no help at all, but sold me a pcb board for about £300 that i still have...

When this little diode packed up, the set still worked perfectly, but every few seconds you would have a violent explosion in the weld pool.

I swapped this for one of the diodes with absolutely nothing wrong with it [that i removed when they sold me a set of the things to replace mine that were perfect to start with] [ Thank you Genset, another stab in the dark from your diagnostic "engineers" [Read twats] [another nearly £600 down the pan] and then the thing worked perfectly..

Having said that, i did use a MOSA one once, and it was MUCH nicer to weld with, so courgette you Genset, i would NEVER buy anything off them EVER AGAIN...

john....

 

[stockers08]

im curious to know how i would get the residual magnetism back.  the rotor has no winding's on it.  its a cage rotor.

i will get some pictures tomorrow.   i have disconnected the output for the welder side incase the diodes were causing a short.  still no change.

i dont care if the welder side never works again.  im not a welder, i want to 240v side to work.  

i have tried magnetizing the stator by putting a car battery across the welder windings in short bursts.  this did nothing.

 

[roys]

i have tried magnetizing the stator by putting a car battery across the welder windings in short bursts.  this did nothing.

That is the usual way of restoring the magnetism, did you do it the correct polarity?

 

[stockers08]

i tried it in both directions.  but no difference.   im not sure i understand how the polarity would make a difference when its ac anyway.   im thinking maybe flash it with 12vac from a transformer.  that way i cant get the wrong polarity and it is ac like the windings will produce

 

[Tony S]

i tried it in both directions.  but no difference.   im not sure i understand how the polarity would make a difference when its ac anyway.   im thinking maybe flash it with 12vac from a transformer.  that way i cant get the wrong polarity and it is ac like the windings will produce

Regulated DC applied to one stator phase winding should magnetically polarise the rotor.

AC applied to the stator will kill any residual magnetism in the rotor so don’t try it.

 

[stockers08]

dc reduced the voltage i was getting from 1.5v to 0.7v.   how would i get the residual back if dc reduces it and ac would kill it?

 

[apprentice87]

You obviously did it wrong.. Do it again, but measure the winding resistance first as a check on how much current flows.. Disconnect the pcb first i would!! Give it about 10 seconds with the battery..

DO NOT use ac as has been mentioned... Ac is how demagnetisers work...... and you do not want to do that...

Is a genset 300amp welder not an expensive way of having an 8KVA generator?? Mine was an 850cc twin cylinder diesel of 23bhp as i remember.. Still used to use about 6 gallons of diesel a day, and, if you are actually using power all that time, a lot more i would think.....

john..

 

[stockers08]

it was cheap from ebay.  (less than £300) i already have the pcb out as it was getting in the way.    even just a momentery blip on the battery created quite a spark.   the resistance across ALL winding's was 0.9 ohms.   

this unit has a 20hp engine as is said to run for 11 hours on a tank of fuel at 75% load.  42l tank.   i doubt i will ever get it to 75% but it gives me the headroom i need for what i want to run from it.

 

[stockers08]

i might have just discovered something using a spare rotor i have.   i knew it had very little residual magnetism, tested using a compass. 

i decided to arch a battery across each end.    it now has a much stronger magnetism,   i might try this on the rotor that is in the generator.

im thinking just that bit more magnetism will get things going. seeing as flashing the stator has not had any effect.

 

[Tony S]

OK this is a bit off topic.

Many moons back we had a 400kW DC set. The bearings in the exciter were shot, we had a spare so simply changed it. Exciter? It was as exciting as a fart. One “little tap” with a sledge hammer got it very excited.

Lines of magnetic flux can be restored by impact. The trouble is, hit it the wrong way and you make matters worse. C'est la vie!

You can try this with the old school boy experiment. Get an iron bar and repeatedly tap it longitudinally it on a hard surface, Voilà, you have a magnet.

 

[apprentice87]

Sounds good to me!!!

john..

 

[binky]

bar needs to be orientated North South, if you hold it East West it demagnetises.

 

[steptoe]

OK this is a bit off topic.

Many moons back we had a 400kW DC set. The bearings in the exciter were shot, we had a spare so simply changed it. Exciter? It was as exciting as a fart. One “little tap” with a sledge hammer got it very excited.

Lines of magnetic flux can be restored by impact. The trouble is, hit it the wrong way and you make matters worse. C'est la vie!

You can try this with the old school boy experiment. Get an iron bar and repeatedly tap it longitudinally it on a hard surface, Voilà, you have a magnet.

Is that a similar effect to rubbing 2 screwdrivers together if you need a magnetic one,? 

 

[binky]

no, you need 'glee' for that, same as your hands

 

[stockers08]

applying a current to the rotor did not work     can a capacitor read good but actually be bad?  thats all i can think of now.

flashing the windings does make the engine slow slightly, so it is obviously having an effect on the rotor.  just it wont build up charge.

the voltage i am getting is reading at 50.8-53hz. so i know the engine is up to speed. 

 

[apprentice87]

You can try this with the old school boy experiment. Get an iron bar and repeatedly tap it longitudinally it on a hard surface, Voilà, you have a magnet

Yes that is right, Apparently you have to hold it upright, hammer the end, and the thing becomes magnetised as the atoms in the thing align themselves with the magnetic field of the earth, presumably as a result of some form of "recovery" type mechanism [As in creep etc]

john..